Mesh doesn't mirror right
Look at the rotation values for your object. Your object is rotated 180 degrees in X and 90 degrees in Z



It was rotated in object mode but the rotation has not been applied.

Apply transformations by pressing Ctrl+A and choose Apply Rotation (but you should really apply Rotation &amp;Scale, so that the scale is applied as well)

Read: Why is it important to apply transformation to an objects data?